Production of olefin polymers



ted rates atent thee 3,012,023 Patented Decu 5, 19 61 3,012,023PRODUCTION OF OLEFlN POLYMERS Arthur William Anderson, Wilmington, JohnMae-Militia Bruce, J12, Ciaymont, and Nicholas George Merckling andWilliam Lawrence Truett, Wilmington, DeL, as-

signors to E. I. du Pont de Nemours and Company,

Wilmington, DeL, a corporation of Delaware No Drawing. Filed Jan. 25,1955, Ser. No. 434,034

12 Claims. (Cl. 260-943) This invention relates to a novel step in theproduction of normally solid ethylene polymers and other polymers ofolefinic compounds containing terminal methylene 2)- In processes whichhave recently been developed for the synthesis of polymeric productsfrom ethylene and/ or other olefinic compounds, in the presence ofpolymerization initiators containing one or more inorganic componentsfor example, an initiator obtained by mixing TiCL, or ZrCl withAl(alkyl) or LiAl(all yl) the reaction product contains titanium orzirconium in such a form that it cannot be separated from the organicpolymeric component by physical means. In many instances the reactionproduct is completely soluble in a liquid hydrocarbon medium, such asxylene, yet contains substantial amounts of titanium (or zirconium)which evidently is present as a component of groups which are attachedto the long polymer chains. The present invention is concerned withchemical methods for separating titanium or zirconium containing groupsfrom the polymeric chain.

It has been discovered, in accordance with this invention, that bysubjecting the above-mentioned polymeric products to the action ofoxygen, or an hydroxyl containing reactant, the titanium or zirconiumbecome readily separable therefrom.

The invention can best be understood by considering the followingreaction mechanism, which, however, should not be construed asrepresenting the only mechanism which can account for the resultsachieved.

In the foregoing formulations n is the number of ethylene units reactingper unit of initiator, X is the group attached to titanium and m is thevalence of titanium. In polymerization wherein the catalyst systemscontain a titanium compound in combination with an aluminum trialkyl, ora lithium aluminum tetraalkyl as a reducing agent, it is the titaniumwhich becomes bonded to the polyethylene chain in preference to thealuminum. This is in contrast with the method for end group removal,described in the Ziegler et al. patent, US. 2,699,547.

Typical initiator systems which are especially eiiective are thoseobtained by admixing a component containing titanium or zirconium,attached to a group such as H, hydrocarbon, oxyhydrocarbon,halohydrocarbon, ha1ide, etc., in combination with a second componenthaving H, or hydrocarbon directly attached to metal. Outstandingexamples of the first component are Ti 1 TiCl Ti(O hydrocarbon).,, andTi(O hydrocarbonh. Outstanding examples of the second component aresodium acetylide, products formed by contacting metallic sodium with analkene higher than ethylene, corresponding products from each of theother alkali metals and alkaline earth metals, alkali metal aluminumhydrides, alkali metal borohydrides, alkaline earth metal hydrides,alkali metal hydrides, alkylaluminum chlorides, alkali metal, aluminumalkyls, alkali metal boroalkyls, Grignard reagents, such asphenylmagnesium halides, etc.

'The conditions for carrying out the polymerization.

I be an alcohol.

reaction can be varied rather widely. In general, the polymerizationtakes place in an inert organic liquid medium such as xylene, toluene,benzene, hexane, isooctane, decane, decalirn, etc., at a pressure whichis sufficient to maintain the reaction medium in the liquid phase. Thepressure can be as low as atmospheric, or as high as 1000 atmospheres,or even higher. Polymerization temperature can be varied Widelydepending in part on the character of the product which is sought.Temperatures within the range of 0 to 300 C. may be used. In general,however, the process of this invention is most effective when used inconjunction with polymerization reactions carried out at 20 to Theremoval of the polymer end groups by the method of this invention takesplace quite rapidly, even at relatively low temperature. In fact, attemperatures of 15 to 50, the reaction is almost instantaneous if theadded reactant is well distributed in the mixture resulting from thepolymerization reaction. In order to facilitate contact between thetitaniun-containing or zirconium-containing group bound to the polymerand the end groupremoving reactant, it is preferable that the saidreactant It is not essential that the alcohol be one which is misciblein all proportions with the reaction medium. For example, methanol ishighly effective even when the reaction medium is a hydrocarbon, such ascyclohexane, which is not completely miscible therewith. The polymericproduct itself need not be dissolved in the reaction medium, and in factis most frequently dispersed in the liquid medium, in the form of aslurry.

If the reactant is water or oxygen, the end group is converted to aninorganic precipitate from which the polymer can be separated byselective solvents, suitably at elevated temperature. On the other hand,if the reactant is an alcohol, and the reaction medium is a hydrocarbon,it has been discovered that the end group is converted to a product(e.g. a titanate ester, or other ester) which goes into solution. Thisis highly advantageous especially in the manufacture of polyethylene,because the polymer is not soluble in any liquid hydrocarbon attemperatures of 15 to 50 0., hence the end groups can be removed in theindicated manner, leaving the solid polymer in a form such that it canbe recovered by simple filtration and removal of adhering liquidhydrocarbon.

In the latter procedure, the filtrate contains the inorganicconstituents which, prior to the alcoholysis, were chemically combinedwith the polymer. These can be converted to insoluble material byoxidation with gaseous oxygen, as a step in the recovery of thehydrocarbon medium, or used again as one of the components of theinitiator as hereinabove described.

The quantity of added end group-removing reactant should be sufiicientto react with the end groups, a stoichiometric quantity being sufiicent.Larger quantities may be used advantageously, but this is not essential,although contact between the reactants is facilitated by using an excessof the alcohol reactant. From one to ten mols of alcohol, or more permol of polymeric product is preferred. It is of course not essential toremove all traces of end group components, although with good contactbetween polymer and end group-removing reactant splitting of the endgroups from the polymer can be achieved quite efiiciently.

Generally the removal of the titanium-containing of zirconium-containinggroups is accompanied by a sudden change in the appearance of thepolymeric product. This occurs whether the end group-removing reactantis oxygen, an alcohol, or Water. The color is generally improved quitemarkedly, and a clean, sometimes colorless, product is formed.

In one method of practicing the invention, the end groups are split fromthe polymer by means of gaseous arator (settler).

oxygen, and no effort is made to remove the inorganic residue from themixture, in which it is allowed to remain as a filler. This of course isnot the preferred method where maximum clarity is desired, but whereclarity is not essential it is a preferred method.

In practical operations using an alcohol as the end group-removingreactant, it is sometimes helpful to intro duce the alcohol reactant inthe form of an azeotrope, distilled from a preceding batch of recoveredhydrocarbon.

The invention is illustrated further by means of the following examples:7

Example 1.-Into 1 liter of cyclohexane is placed 3.9 rnillimols TiCl and1.3 millimols of LiAl(heptyl) Ethylene is introduced into the resultingmixture with stirring for 2 hours at 50 C., producing about 65 grams ofa polymeric product in the form of a slurry. The polymeric product thusformed contains nearly all of the initiator. The slurry is cooled to 25C., and 10 cc. dry isopropanol is added with continued stirring. Theslurry is filtered, yielding a polymer which is virtually ash-free. Thefiltrate contains the titanium in dissolved form; on exposure to air thefiltrate yields a precipitate of titania.

Exam le 2.-lnto 1 liter of cyclohexane is placed 6 millimols TiCl and 2millimols LiAl(decyl) Ethylene is introduced into the resulting mixturewith stirring for 2.5 hours at 40 to 47 C., producing a slurrycontaining about 86 grams of polymeric product. The polymeric productthus formed contains nearly all of the initiator. This mixture is cooledto 25 C. and 10 cc. dry methanol is added with continued stirring. Theslurry is filtered, yielding a polymer which is virtually ash-free. Thefiltrate contains the titanium in dissolved form; on exposure to air thefiltrate yields a precipitate of titania.

Example 3.-Into 1 liter of cyclohexane is placed 6 miilimols ZrCl and 2milli'mols of sodium acetylide. Ethylene is introduced into theresulting mixture with stirring for 10 minutes at 35 C. To the resultingslurry cc. n-butanol is added, and the mixture is filtered, yieldingpolyethylene which is virtually free of zirconia.

Example 4.Into 200 cc. of cyclohexane' is placed millimolstetra(2-ethylhexyl)titanate and ml. of a 3 M ethereal solution ofphenylmagnesium bromide. Ethylene is introduced into the resultingmixture for 2 hours at 30 C. at a pressure of 500 lbs. per square inch.The resulting slurry is agitated with 5 cc. of added methanol andfiltered, yielding polymer which contains relatively little titanium. Inrepeating the experiment without the added alcohol, most of the titaniumremains with the polymer.

Example 5.Ethylene is polymerized at 170 C. to 190 C. for 2 hours at7501000 p.s.i. in the presence of 2.3 grams TiCl and 0.86 gram AI(CH in27 ml. cyclohexane, yielding 46 grams of polyethylene. When the productis subjected to the action of steam, the hydrocarbon portion isselectively soluble in boiling benzene, and the inorganic portion isnot.

Example 6.-A solution of 0.04 M TiCl in cyclohexane is stored in astainless steel tank under nitrogen pressure. Another solution, composedof 0.03 M LiAl(heptyl) in cyclohexane is similarly stored in a stainlesssteel tank. Streams from each or" these tanks are united at 50 C. in theproportion of l to 1. The combined stream is diluted with 5 times itsvolume of cyclohexane and pumped continuously through a stainless steelreactor which is equipped with a stirrer, an ethylene inlet means, and awater cooler for withdrawal of heat. Ethylene is introduced into themixture at the rate of 6 liters per minute at atmospheric pressure withvigorous agitation, maintaining temperature at 4050 C. The poly- Imerization proceeds readily, yielding a slurry which is continuouslywithdrawn from the reactor into a solids sep- The solids'remain in thereceiver, and the liquid is drawn from it. The solid is placed on alarge Buchn-er funnel, and air is sucked through the solid for about 5minutes to kill the catalyst and improve the color of the product(chemically separating the end groups from the polyethylene chain). Theresulting product is a white powder containing small amounts of solvent,which are subsequently removed by evaporation. When melted, the productis not transparent.

The foregoing examples are illustrative only, and numerous modificationsof the invention will be apparent to those who are skilled in the art.For instance, the mol ratio of LiAl(alkyl) :Ti-Cl can be varied withvariation in the results obtained. At relatively low pressures {l to 5atmospheres) and relatively low temperatures (20 to C.) this ratioshould be within the range of 0.3: 1.0 to 0.8: 1. 0 to obtainpolyethylene having a melt index of from 10.0 to about 0.01, which is ahighly desirable commercial range. With higher proportions ofLiAl(alkyl) the melt index is lowered (i.e. molecular weight isapparently increased) to such an extent that the workability, orshaping, of the polymer requires methods differing from those currentlyin use for polyethylene. If the proportion of LiAl(alkyl) is too low,the molecular weight is low, and product quality (for plasticsapplications) suffers.

Moreover, numerous methods for recovering catalyst can be based on thepresent invention. Zirconium compounds, which are expensive but whichare among the best catalysts, can, for example, be recovered andre-used, while cheaper materials such as titanium-containing groups canbe removed by the process of this invention without any need forsalvaging the titania.

The process of the invention can be conducted batchwise or continuously.

Catalysts for the sclvolysis of the end groups can be used if desired,but the reaction is generally rapid enough in the absence of catalysts.Hydrogen chloride may be present during the removal of the end groups,and, when present, may indeed take part in the reaction. Hydrogenchloride can be formed in situ under conditions such that a componentsuch as free TiCl undergoes hydrolysis or alcoholysis. To improvecontact of such agents as HCl with the polymer undergoing treatment, anoxygenated organic solvent, such as acetone, can be introduced ifdesired.

Thus, since many different embodiments of the invention will occur tothose who are skilled in the art, it is to be understood that theinvention is not limited by the specific illustrations hereinabove setforth.

This application is a continuation-in-part of our copending applicationSerial No. 450,243, filed August 16, 1954, now US. Patent 2,905,645.

What is claimed is the following:

1. In a process for preparing normally solid polyethylene bypolymerizing ethylene in an inert hydrocarbon liquid medium and in thepresence of an initiator which supplies groups'having an element of theclass consisting of titanium and zirconium attached directly to thepolymer, said initiator being the product obtained by admixing acomponent containing a member of the class consisting of titanium andzirconium, attached to a group of the class consisting of-oxyhydrocarbon and -halide, with a second component having -hydrocarbonattached directly to metal, said metal being of the class consisting ofalkali metals, alkaline earth metals and aluminum, the improvement whichcomprises removing such groups from the polymer moleculeby reaction withwater.

2. In a process for preparing normally solid polyethylene bypolymerizing ethylene in an inert hydrocarbon liquid medium and in thepresence of an initiator which supplies groups having an element of theclass consisting of titanium and zirconium attached directly to thepolymer, said initiator being the product obtained by admixing acomponent containing a member of the class consisting of titanium andzirconium, attached toa group of the class consisting of -oxyhydrocarbonand -halide, with a second component having -hydrocarbon attacheddirectly to metal, said metal being of the class consisting of alkalimetals, alkaline earth metals and aluminum, the improvement whichcomprises removing such groups from the polymer molecule by reactionwith an alkanol having from 1 to 4 carbon atoms per molecule.

3. Process of claim 2 wherein the quantity of said alkanol added is fromone to ten mols per equivalent of said group.

4. Process of claim 2, wherein the said polymerization takes place at atemperature of 20 to 150 C., and reaction of the said alkanol and thesaid polymer takes place at a temperature below the polymerizationtemperature and in the range of 15 to 50 C.

5. Process of claim 2 wherein the said initiator is the product obtainedby admixing TiCL; with a metal-hydrocarbon compound in an inert liquidhydrocarbon medium.

6. Process of claim 5 wherein said metal-hydrocarbon compound is alithium aluminum tetraalkyl.

7. Process of claim 5 wherein said metal-hydrocarbon compound i analuminum trialkyl.

8. Process of claim 2 wherein the said alkanol is added to the polymerin the form of a slurry containing the said inert liquid hydrocarbonmedium, whereby the said groups are removed from said polymer.

9. Process of claim 8, wherein the reaction of the said alkanol and thesaid polymer takes place at a temperature in the range of 15 to 50 C.

10. In a process for preparing normally solid polyethylene bypolymerizing ethylene in an inert hydrocarbon liquid medium and in thepresence of an initiator which supplies groups having an element of theclass consisting of titanium and zirconium attached directly to thepolymer, said initiator being the product obtained by admixing acomponent containing a member of the class consisting of titanium andzirconium, attachedto a group of the class consisting of -oxyhydrocarbonand halide, with a second component having hydrocarbon attached directlyto metal, said metal being of the class consisting of alkali metals,alkaline earth metals and aluminum, the improvement which comprisesremoving said groups from the polymer molecule by reaction withmolecular oxygen until the catalyst is inactive, and thereafterrecovering from the resulting mixture the polymer devoid ofcatalytically active material.

11. In a process for preparing hydrocarbon polymers by polymerization inthe presence of an initiator which supplies metal-containing groups tothe polymer, said 6 initiator being the product obtained by admixing acomponent containing a member of the class consisting of titanium andzirconium, attached to a group of the class consisting of-oxyhydrocarbon and -halide, with a second component having -hydrocarbonattached directly to metal, said metal being of the class consisting ofalkali metals, alkaline earth metals and aluminum, the improvement whichcomprises removing such groups from the polymer molecule by means of areactant which is capable of splitting metal-hydrocarbon bonds, saidmetal being a member of the class consisting of titanium and zirconium,said reactant being of the class consisting of oxygen, water, andalcohols of the formula C I-I OH wherein n is a number from 1 to 4inclusive.

12. In a process for preparing normally solid polyethylene bypolymerizing ethylene in the presence of an initiator which suppliesmetal-containing groups to the polymer, said initiator being the productobtained by admixing a component containing a member of the classconsisting of titanium and zirconium, attached to a group of the classconsisting of -oxyhydrocarbon and -halide, with a second componenthaving -hydrocarbon attached directly to metal, said metal being of theclas consisting of alkali metals, alkaline earth metals and aluminum,the improvement which comprises removing such groups from the polymermolecule by a reactant which is capable of splitting metal-hydrocarbonbonds, said metal being a member of the class consisting of titanium andzirconium, said reactant being of the class consisting of oxygen, water,and alcohols of the formula C H OH wherein n is a number from 1 to 4inclusive.

References Cited in the file of this patent UNITED STATES PATENTS2,453,520 Langkammerer Nov. 9, 1948 2,682,531 Ernst et al June 29, 19542,683,139 Leary et al. July 6, 1954 2,699,457 Ziegler et al. Jan. 11,1955 2,905,645 Anderson et al Sept. 22, 1959 OTHER REFERENCES Chem.Reviews, vol. 17 (1935) (Galloway), pp. 327 and 374-377.

Herman et al.; I. Am. Chem. Soc. 75, 3877-3882 (Aug. 20, 1953).

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No,3,012,023 December 5 1961' Arthur William Anderson et a1,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 19, before "for" insert an opening peren thesis; line 48,for polymerization" read polymerizations column 2 line 64, for "of",second occurrence, read or Signed and sealed this 24th day of April1962,

(SEAL) Attest:

ESTON G. JOHNSON DAVID L, LADD Attesting Officer Commissioner of Patents

12. IN A PROCESS FOR PREPARING NORMALLY SOLID POLYETHYLENE BYPOLYMERIZING ETHYLENE IN THE PRESENCE OF AN INITIATOR WHICH SUPPLIESMETAL-CONTAINING GROUPS TO THE POLYMER, SAID INITIATOR BEING THE PRODUCTOBTAINED BY ADMIXING A COMPONENT CONTAINING A MEMBER OF THE CLASSCONSISTING OF TITANIUM AND ZIRCONIUM, ATTACHED TO A GROUP OF THE CLASSCONSISTING OF -OXYHYDROCARBON AND -HALIDE, WITH A SECOND COMPONENTHAVING -HYDROCARBON ATTACHED, DIRECTLY TO METAL, SAID METAL BEING OF THECLASS CONSISTING OF ALKALI METALS, ALKALINE EARTH METALS AND ALUMINUM,THE IMPROVEMENT WHICH COMPRISES REMOVING SUCH GROUPS FROM THE POLYMERMOLECULE BY A REACTANT WHICH IS CAPABLE OF SPLITTING METAL-HYDROCARBONBONDS, SAID METAL BEING A MEMBER OF THE CLASS CONSISTING OF TITANIUM ANDZIRCONIUM, SAID REACTANT BEING OF THE CLASS CONSISTING OF OXYGEN, WATER,AND ALCOHOLS OF THE FORMULA CNH2N+1OH WHEREIN N IS A NUMBER FROM 1 TO 4INCLUSIVE.